Human lymphocytes will be studied to determine how the various lymphycyte immune functions are mediated through membrane-bound receptors. Complement receptors and the lymphocytes to which they are attached will receive special emphasis. Various combinations of double-label assays for all of the known lymphocyte receptors will be utilized in an attempt to define important lymphocyte subpopulations in terms of their content of different types of receptors. If possible, the individual stages of lymphocyte maturation, activation and aging will be classified in terms of the order of appearance and disappearance of receptors. Normal lymphocytes will be studied and compared for receptor content and function with lymphocytes obtained from patients with rheumatoid arthritis, various forms of lymphoma, and mammary carcinoma. In rheumatoid arthritis, B cell surface immunoglobulin will be analyzed for IgG specificity and, in addition, joint fluid will be studied to determine if it activates lymphocytes by way of their complement receptors. With different forms of lymphoma, an attempt will be made to subclassify each basic form by characteristic receptor-bearing lymphoid cells. The clinical history of the lymphoma patients will then be examined to determine if any of the subclassifications of a particular form of lymphoma have any correlations with prognosis or therapy. Lymphocytes from patients with various stages of mammary carcinoma will be examined to determine if receptor deficiencies exist which might contribute to a depression of their cellular immunity.